Stegosaurus, the "Roofed Lizard," is the most famous member of the Stegosauridae family, which is known for its unique body armor consisting of plates and spines. Stegosaurus is  also the largest in its family at  almost nine meters long and four  meters tall. Originally depicted  with its plates laying flat on its back like roof tiles, the famous  plates of the Stegosaurus stood up  on its back in two offset rows. The purpose of these plates is still  debated, but they were likely for  sexual display, thermoregulation, or intimidation. The spikes on its tail  are known as "thagomizers," a name  popularized by Gary Larson's Far  Side comic. As its main source of  defense, the tail could be swung  with great force at foes, goring  them with the sharp spikes.  Living alongside Allosaurus in Late Jurassic United States and Portugal, Stegosaurus had good reason to have such a strong defensive system. It  was one of Allosaurus's many food  sources, so fighting back against  the mighty predator was a necessity. It was successful, too; one  Allosaurus fossil contains a  puncture would that almost  certainly came from a thagomizer. When it wasn't protecting itself,  Stegosaurus travelled in herds eating low-level plants like  mosses or fruit. Rearing on its hind legs would let it reach heights of  up to six meters.